Frequency domain polarimeter

ABSTRACT

The total energy, wave type, orientation and rotation of an incident electromagnetic signal having an unknown polarization is identified through single channel frequency domain signal analysis of the incident electromagnetic wave power as measured by an orthogonally polarized electromagnetic sensor. A controlled switch samples between the power measurements at each orthogonal output of the sensor to generate a signal comprised of a carrier frequency component and two sideband frequency components in the frequency domain. The sampled radio frequency signal is down converted by a single channel receiver to an intermediate frequency where the carrier and one sideband frequency component are separated and coherently shifted to the same frequency. A phase detector and ratiometer measure the relative phase and amplitude differences between the separated carrier and sideband frequency components to identify the wave type, orientation and rotation of the incident electromagnetic signal. In addition to identifying the type, orientation and rotation of the incident electromagnetic wave, the total energy of the incident polarized electromagnetic wave is determined using a single channel polarization diversity system or a single channel polarization insensitive system.

RELATED APPLICATION

This application is a continuation-in-part of application Ser. No.07/827,414, filed Jan. 29, 1992, now U.S. Pat. No. 5,235,340.

TECHNICAL FIELD

The present invention relates to measuring electromagnetic wave energy,and more particularly to an apparatus for measuring the polarization ofan incident electromagnetic signal.

BACKGROUND OF THE INVENTION

It is well-known in the art that electromagnetic waves in the radiofrequency spectrum may be linearly, elliptically or circularlypolarized. Linearly polarized electromagnetic waves are confined to asingle plane extending in the direction of wave propagation and may beoriented at any angle. Electromagnetic waves that are either circularlyor elliptically polarized comprise a linear wave rotated about the axisof wave propagation in either a clockwise or counter-clockwise manner.The major axis of an elliptically polarized wave may be orientated atany angle in a manner similar to a linearly polarized wave.

In military applications, it is important that information on theincident electromagnetic wave type, that is, orientation and rotation,be determined as quickly as possible. This information provides animportant parameter identifying the signature, or fingerprint, of theelectromagnetic wave emitter. Once the wave information has beenidentified, the emitter that generated the incident electromagnetic wavecan be recognized from its signature for purposes of intelligencegathering, homing, emitter sorting, interference reduction, orconfiguration of an active electromagnetic wave jammer.

Historically, polarimeters have been constructed of a dual channelreceiver coupled to a dual orthogonally polarized antenna to measure thepower of the polarization components of the incident electromagneticwave. The measured power of these components identifies the polarizationcharacteristics of the electromagnetic waves. A conventional polarimetercomprises an orthogonally polarized antenna coupled to a pair of phaseand gain matched receivers. Identification of the type, orientation androtation of the incident wave is accomplished by comparing the relativeamplitude and phase of the output signals from the dual receivers.

In addition to identifying the type, orientation, and rotation of theincident electromagnetic wave, a polarimeter system must be capable ofsensing the total energy in the incident polarized electromagnetic wavewith as little energy loss as possible. In conventional dual channelreceivers, a dual orthogonally polarized antenna receives from zero toone hundred percent of the energy in an incident polarizedelectromagnetic wave depending on the antenna's coupling coefficient tothe electromagnetic wave's polarization. The pair of phase and gainmatched receivers of the conventional dual channel receiver individuallyoutput two separate signals representing the energy in each of the twoorthogonally polarized wave components. These two orthogonally polarizedwave components always sum to one hundred percent of the incidentpolarized electromagnetic wave's energy if there is no energy loss inthe system. The lower the energy loss in the system during the recoveryof the energy of the incident polarized electromagnetic wave the greaterwill be the signal to noise ratio.

This conventional approach to polarimeter construction has proven to beunsatisfactory as it requires interconnecting two complex and costlyphase and gain matched receivers. A further drawback of dual channelmatched receiver polarimeters is that the second receiver adds weight tothe apparatus and requires additional mounting space. In weight andspace sensitive applications, for example, in military aircraft, theweight and space necessary to provide a second receiver for thepolarimeter may not be available or, if available, is provided at theexpense of other important system components.

Accordingly, there is a need for a signal processing technique forpolarization detection that eliminates the need for complex and costlydual channel receivers. There is also a need for a signal processingtechnique for a polarization detection system that senses the totalenergy in the incident polarized electromagnetic wave without the needfor complex and costly dual channel receivers.

SUMMARY OF THE INVENTION

The present invention overcomes the foregoing problems and otherproblems associated with conventional polarimeter construction byproviding a signal processing technique utilizing a single channelreceiver to detect wave characteristics and identify emitter signatures.In accordance with the broader aspects of the invention, the incidentelectromagnetic wave power is measured and output by an orthogonallypolarized electromagnetic sensor. The output electromagnetic power fromeach sensor is processed by a single channel receiver for phase andamplitude comparison. The phase and amplitude comparison information isthen further processed to identify the type (linear, circular orelliptical), orientation (polarization angle) and/or rotation (clockwiseor counter-clockwise) of the incident electromagnetic wave. In additionto identifying the type, orientation, and rotation of the incidentpolarized electromagnetic wave, the signal processing technique of thepresent invention utilizes a single channel receiver to sense the totalenergy in the incident polarized electromagnetic wave. The total energyis the sum of the energy received simultaneously in the two orthogonallypolarized components.

In particular, the orthogonally polarized sensor outputs are connectedto a single-pole, double-throw radio frequency (RF) sampling switchdriven by a stable squarewave oscillator operating at a samplingfrequency equal to at least twice the bandwidth of the incoming signal.The RF output from the sampling switch consists of a carrier frequencycomponent and two sideband components in the frequency domain producedby the interaction between the incident wave polarization and themodulating signal action of the sampling RF switch. The output of the RFswitch is connected to a single channel receiver and down converted toan intermediate frequency (IF) output for further signal processing. Thecarrier and sideband frequency components are separated using bandpassfilters and coherently shifted to the same frequency. Relative phase andamplitude between the shifted frequency components is then measured andcompared to uniquely identify the polarization signature of the incidentelectromagnetic wave.

In the alternative, a polarization diversity system using the signalprocessing techniques of the present invention compares the relativeamplitudes of the carrier and sideband frequency components and outputthe component which has the greatest amplitude. This polarizationdiversity system would result in a sensitivity which should not bedegraded by more than 3 dB due to polarization. A conventional singlepolarized receiving system will sometimes fade more than 30 dB due tobeing cross polarized.

In another alternative, a polarization insensitive system using thesignal processing techniques of the present invention compares the phasedifference between the carrier and sideband frequency components. Afterthe phase differential is determined, the carrier frequency component isphase shifted such that it is in-phase with the sideband frequencycomponent. It will be understood that either a separated sidebandfrequency component or the carrier frequency component may be shiftedsuch that the two components are in-phase. Once the carrier frequencycomponent and the sideband frequency component are in-phase, thecomponents are summed in a coupler to recover the total energy of theincident polarized electromagnetic wave, providing maximum sensitivityto the received signal with regard to polarization.

Possible applications for the apparatus of the present invention includeelectromagnetic intelligence gathering, multiple emitter sorting andrecognition, calibration of homing systems, instrument sensitivityenhancement and interference reduction, and polarization configurationof active electromagnetic jammers. Other advantages in applicationsderiving from the use of the invention will readily suggest themselvesto those skilled in the art from consideration of the following DetailedDescription taken in conjunction with the accompanying Drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the invention may be had by referenceto the following Detailed Description when taken in conjunction with theaccompanying Drawings wherein:

FIG. 1 is a block diagram for a conventional dual channel matchedreceiver polarimeter;

FIG. 2 is a simplified block diagram for a single channel receiverfrequency domain polarimeter;

FIG. 3 is a block diagram showing the preferred embodiment for thesingle channel receiver frequency domain polarimeter;

FIG. 4 is a block diagram for a single channel receiver polarizationdiversity system; and

FIG. 5 is a block diagram for a single channel receiver polarizationinsensitive system.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring now to FIG. 1, there is shown a block diagram for aconventional dual channel phase and gain matched receiver polarimeter 10for measuring wave type, orientation and/or rotation of an incidentelectromagnetic wave, generally indicated by an arrow 12. Anorthogonally polarized antenna, schematically represented by two linearprobes 14 and 16 measures the RF power of the incident wave 12. A pairof phase and gain matched receivers 18 and 20 are coupled to theorthogonal probes 14 and 16 respectively. A shared local oscillator 22is connected to each matched receiver, 18 and 20, to down convert the RFsignal measured by probes 14 and 16 to an IF signal. A phase detector 24and ratiometer 26 compare the IF signals output from the matchedreceivers 18 and 20 to determine the polarization signature of theincident wave 12.

Referring now to FIG. 2, there is shown a block diagram for a singlechannel receiver frequency domain polarimeter 30 of the presentinvention for measuring the wave type, orientation and/or rotation of anincident polarized electromagnetic wave 12. An RF pickup 32 is utilizedby the polarimeter 10 to measure the RF power of the incident wave 12.RF pickup 32 is comprised of a pair of orthogonal linear electromagneticprobes 34 and 36. It will be understood, of course, that any othersuitable means may be provided for measuring orthogonally polarized RFpower components of the incident wave 12.

A pair of RF conductors 38 and 40, for example, coaxial cables, couplethe RF power measured by probes 34 and 36 to a single-pole, double-throwRF sampling switch 42. RF switch 42 is comprised of a pair of contactpoints 44 and 46 connected to the RF conductors 38 and 40 respectively.Switch 42 further comprises a controlled gate 48 that is switchedbetween contacts 44 and 46 to sample the RF power from probes 34 and 36.The sampled RF power is coupled from gate 48 to an RF output conductor50. Sampling movement of gate 48 is controlled by an input square wavegenerated by a fixed frequency square wave oscillator 52 and coupled toswitch 42 through line 54. The fixed oscillation frequency of the squarewave output by oscillator 52 is selectively chosen to cause switch 42 tosample the RF power at probes 34 and 36 at a frequency at least twotimes the bandwidth of the incoming signal.

Modulation of the incident wave 12 through the square wave sampling ofswitch 42 produces an output RF signal on conductor 50 comprised of acarrier frequency component and two sideband frequency components in thefrequency domain. The frequency domain spectrum of the signal at theoutput of the switch 42 is a function of the polarization of incidentelectromagnetic signal and the switching frequency as shown below.

As is well known, the instantaneous electric field vector E of anincident plane wave 12 of unknown polarization may be written as:

    E=E.sub.1 e.sup.jwt i+E.sub.2 e.sup.jwt+β k           (1)

wherein:

E₁ =peak amplitude of the electric field in x-direction i;

E₂ =peak amplitude of the electric field in y-direction k; and

β=phase by which the y-component of the electric field leads thex-component.

The relationship between E₁, E₂ and β defines the polarization type,orientation and rotation of the incident electromagnetic signal in amanner well known. Table 1 shows some selected examples of the manner inwhich E₁, E₂ and β influence polarization signature (type, orientationand rotation).

                  TABLE 1                                                         ______________________________________                                        E.sub.1 E.sub.2                                                                              β    Polarization Signature                               ______________________________________                                        1       0      --        Horizontal                                           0       1      --        Vertical                                             1       1      0         slant linear (45°)                            1       1       180°                                                                            slant linear (-45°)                           1       1      +90°                                                                             clockwise circular                                   1       1      -90°                                                                             counter-clockwise circular                           1         0.5  +90°                                                                             clockwise elliptical                                   0.5   1      -90°                                                                             counter-clockwise elliptical                         ______________________________________                                    

Using dual orthogonal linear probes and a single-pole, double throwswitch, the power of the x- and y- components of the electric field isalternatively measured and sampled. The received electric field signalE_(r) (t) output on conductor 50 from switch 42 may be written as:

    E.sub.r (t)=E.sub.1 e.sup.jwt S(t)+E.sub.2 e.sup.jwt+β S(t-T/2)(2)

wherein: ##EQU1## represent the sampling action of switch 42.

In the frequency domain (G) , E_(r) (t) is comprised of a carrierfrequency component and two sideband frequency components, and may bewritten after a β/2 phase shift as:

    G.sub.R (w)=F[E.sub.1 e.sup.jwt-β/2 ]*F[S(t)]+F[E.sub.2 e.sup.jwt+β/2 ]*F[S(t-T/2)]                          (3)

wherein: F represents the Fourier Transform operation.

This frequency domain representation contains the polarizationinformation (E₁, E₂ and β) to be manipulated by the frequency domainpolarimeter 30 of the present invention to identify wave type,orientation and rotation in a manner to be described.

A single channel RF receiver 56 down converts the high frequency RFoutput signal on conductor 50 to an IF signal continuing to be comprisedof a carrier and two sideband frequency components in the frequencydomain. As is well known, down converting of a signal merely shifts thesignal in the frequency domain without altering its frequency domaincharacteristics. The IF signal output by receiver 56 is connected to aprocessing unit 58 where the carrier and one sideband frequencycomponent are separated and coupled to two processing conductors, 60 and62, respectively.

The polarization signature (wave type, orientation and rotation) is thenidentified from the frequency domain characteristics by a phase detector64 and a ratiometer 66 by measuring E₁, E₂ and β. Phase detector 64coherently shifts the separated carrier and sideband frequencycomponents to the same frequency and measures the phase difference (β)between the components. Detection of the phase difference (β) identifiesthe rotational characteristics of the incident wave 12 in a manner wellknown in the art. Ratiometer 66 measures the relative amplitude betweenthe separated carrier (E₁) and sideband (E₂) frequency component.Detection of the relative amplitude (E₁ /E₂) identifies the wave typeand orientation of the incident wave 12 in a manner well known in theart. Thus, the frequency domain polarimeter 30 uniquely identifies anddefines the polarization signature of the incoming signal utilizing asingle channel receiver and frequency domain signal processor.

Referring now to FIG. 3, wherein like reference numerals refer to likeor similar parts, there is shown the preferred embodiment for thefrequency domain polarimeter 30. The RF pickup 32 comprises a hornantenna 68 and rectangular wave guide 70 terminated by a pair oforthogonal linear electromagnetic probes 34 and 36. It will beunderstood, however, that any other suitable antenna and/or wave guidestructure may be substituted for the horn 68 and rectangular wave guide70 to enable measurement of RF power provided that the sensor includesorthogonally polarized outputs.

A pair of RF conductors 38 and 40 couple the RF power measured by probes34 and 38 respectively to an RF switch 72 that may comprise a PIN diodeswitch and driver. RF switch 72 alternately samples the RF power onconductors 38 and 40 and couples the sampled power measurements to an RFoutput conductor 50. A driver signal generated by a switching oscillator52 on line 54 controls the sampling function of the RF switch 72. Theswitching signal output by oscillator 52 preferably comprises a squarewave with a frequency at least two times the bandwidth of the incidentsignal.

Modulation of the incident wave 12 with the square wave sampling ofswitch 72 produces an RF output signal on conductor 50 comprised of acarrier and two sideband frequency components in the frequency domain.The characteristics of the frequency domain representation of the RFsignal output from switch 72 are determined by the unknown polarizationof the incident wave 12 and the switch modulation. Polarizationinformation, including wave type, orientation and rotation, is extractedfrom the frequency domain representation of the sampled incident wave bycomparing the relative amplitude and phase of the generated carrier andsideband frequency components.

A single channel receiver 56, comprised of an RF amplifier 74, anadjustable frequency local oscillator 76 and a mixer 78, is used to downconvert the RF signal to an IF signal for further frequency domainprocessing. The IF signal output from mixer 78 is still comprised of acarrier and two sideband frequency components as mixing of the RF outputsignal on conductor 50 with the local oscillator merely shifts the RFfrequency spectrum to the IF spectrum to enable further frequencyprocessing and identification of the polarization signature of theincident wave.

The IF signal is then processed by a pair of tuned bandpass filters 80and 82 to separate the carrier and one sideband frequency component ontotwo conductors 60 and 62 respectively. Although filter 82 is shown tunedto separate out the lower sideband frequency component, it will beunderstood that equivalent polarization signature information may beextracted through separation of either the upper or lower sidebandfrequency component. The separated carrier frequency component on line60 is coherently shifted to the same frequency as the sideband frequencycomponent by mixing the separated carrier with the square wave signalgenerated by the switching oscillator 52. Although mixer 84 is shownmixing the carrier frequency component with the switching oscillatorfrequency, it will be understood that either separated sideband orcarrier frequency component may be mixed to coherently shift thecomponents to the same frequency. A filter 86, tuned to the lowersideband frequency component, passes the shifted carrier frequencycomponents out of the processing unit 58.

The amplitude of the separated and coherently shifted carrier andsideband frequency components output from the processing unit 58 is thenmeasured by a pair of logarithmic amplifiers 88 and 90 respectively.Amplitude information on the separated carrier and sideband frequencycomponents is output over lines 92 and 94 respectively foridentification of wave type and orientation of the incident wave in amanner well known. A second set of output lines 96 and 98 pass theseparated carrier and sideband frequency components to a phase detectorsection 64 of the polarimeter. Phase comparator 100 of the phasedetector section 64 measures and compares the relative phase between thecoherently shifted frequency components. This information is output overlines 102 and 104 and processed in a manner well known in the art toidentify the rotation of the incident wave.

A system interface 106 receives the amplitude and phase information overlines 92, 94, 102 and 104 for processing to identify the polarization ofthe incident wave 12 in the manner shown in Table 1. Signals output overlines 88 and 90 relate to the vertical (E₁) and horizontal (E₂) electricfield amplitudes. Signals output over lines 102 and 104 relate to thephase (β) between the field components.

Referring now to FIG. 4, there is shown a block diagram for analternative embodiment of the invention. The alternative embodiment is asingle channel receiver polarization diversity system 110 forsimultaneously sensing the energy in two orthogonally polarizedcomponents of the incident polarized electromagnetic wave 12 andoutputting the component with the greater energy.

As in previously described embodiments, an RF pickup 32 is utilized bythe polarization diversity system 110 to receive the incident polarizedelectromagnetic wave 12. The RF pickup 32 includes a pair of orthogonallinear electromagnetic probes 34 and 36. It will be understood, ofcourse, that any other suitable means may be provided for measuringorthogonally polarized RF power components of the incident polarizedelectromagnetic wave 12.

A pair of RF conductors 38 and 40, for example, coaxial cables, couplethe RF power measured by probes 34 and 36 to a single-pole, double-throwRF sampling switch 72. RF sampling switch 72 is coupled to a switchingoscillator 52 which outputs a fixed frequency square wave selectivelychosen to cause the RF sampling switch 72 to sample the RF power at afrequency at least two times the bandwidth of the incident polarizedelectromagnetic wave 12.

The modulation of the incident polarized electromagnetic wave 12 throughthe square wave sampling of RF sampling switch 72 produces an output RFsignal on conductor 50 comprised of a carrier frequency component andtwo sideband frequency components in the frequency domain. The singlechannel RF receiver 56 down converts the high frequency RF output signalon conductor 50 to an IF signal continuing to be comprised of a carrierand two sideband frequency components in the frequency domain. The IFsignal output is connected to a processor 58 where the carrier frequencycomponent and a sideband frequency component are separated. In theprocessor 58, the carrier frequency component is coherently shifted tothe same frequency as the sideband frequency component. It will beunderstood that either the carrier frequency component or the sidebandfrequency component may be coherently shifted to the same frequency. Thecoherently shifted carrier frequency component is output on line 111 andthe sideband frequency component is output on line 112.

Lines 111 and 112 are coupled to a first detector 113 and seconddetector 114, respectively. The first detector 113 coupled to line 111carrying the coherently shifted carrier frequency component outputs avoltage signal proportional to the energy level of the coherentlyshifted carrier frequency component. The second detector 114 coupled toline 112 carrying the sideband frequency component outputs a voltagesignal proportional to the energy level of the sideband frequencycomponent. The output of first detector 113 and the output of seconddetector 114 are coupled to an amplitude comparator 115. The amplitudecomparator 115 compares the relative amplitude of the outputs bydetector 113 and detector 114 and generates a signal on line 116 thatdrives a single-pole double-throw switch 117 to the larger amplitudecomponent on line 111 and line 112. The largest received component isoutput from the single channel receiver polarization diversity system ofthe present invention on line 118 and may be coupled to a demodulator130 or other device for purposes of additional signal processing. Withthis approach, the sensitivity of the single channel receiverpolarization diversity system 110 will experience degraded performanceby no more than 3 dB due to polarization.

Referring to FIG. 5, a still further embodiment of the present inventionis a single channel receiver polarization insensitive system 120. The RFpickup 32, the single-pole double-throw RF sampling switch 72, theswitching oscillator 52, the single channel receiver 56, and thepolarimeter processor 58 are the same as in previously describedembodiments of the present invention. Line 121 carrying the coherentlyshifted carrier frequency component and line 122 carrying the sidebandfrequency component are coupled to a phase detector 123. The phasedetector 123 detects the phase differential between the carrierfrequency component and the sideband frequency component. The phasedetector 123 then outputs a signal on line 124 responsive to the phasedifferential between the carrier frequency component and the sidebandfrequency component. Line 124 is coupled to phase shifter 125 which, inresponse to the signal on line 124, shifts the phase of the sidebandfrequency component on line 122 such that the carrier frequencycomponent and the sideband frequency component are in-phase. It will beunderstood that either the sideband frequency component on line 122 orthe carrier frequency component on line 121 may be shifted by a phaseshifter to get the two components in-phase. The phase shifter outputsthe in-phase sideband frequency component on line 126 which is coupledto a summer 127 comprises a 3 dB coupler. Summer 127 adds the carrierfrequency component on line 121 to the phase shifted sideband frequencycomponent on line 126 to sense the total energy in the incidentpolarized electromagnetic wave 12. The output from the single channelreceiver polarization insensitive system on line 128 may be coupled to ademodulator 130 or other device for purposes of additional signalprocessing. Such a system provides maximum sensitivity to the receivedpolarized electromagnetic wave 12 with regard to polarization. With thisapproach, the sensitivity of the system will experience degradedperformance by no more than the losses in the system and no degradationdue to polarization.

Although a preferred embodiment of the invention has been illustrated inthe accompanying Drawings and described in the foregoing DetailedDescription, it will be understood that the invention is not limited tothe embodiment disclosed but is capable of numerous rearrangements andmodifications of parts and elements without departing from the scope ofthe invention.

I claim:
 1. Apparatus for processing an incident electromagnetic signal,comprising:means for identifying the orthogonal components ofelectromagnetic power in an incident electromagnetic signal; means forsampling the orthogonal electromagnetic power components to output on asingle channel a sampled signal comprising a carrier frequency componentand two sideband frequency components in the frequency domain; means forseparating the carrier frequency component from the sideband frequencycomponents; means for comparing the relative amplitude of the carrierfrequency component and one of the sideband frequency components; andmeans responsive to the comparison for outputting the component with thelarger amplitude.
 2. The apparatus of claim 1 wherein said means foridentifying comprises a dual orthogonally polarized electromagneticsensor.
 3. The apparatus of claim 1 wherein said means for samplingcomprises:a single-pole, double-throw switch coupled to receive theidentified orthogonal electromagnetic power components and output thesampled signal; and a switching oscillator connected to said switch tocause the switch to sample between the identified orthogonal powercomponents.
 4. The apparatus of claim 1 wherein said means forseparating comprises:a first filter for receiving the sampled signal,bandpass tuned to separate out the carrier frequency component; and asecond filter for receiving the sampled signal, bandpass tuned toseparate out one sideband frequency component.
 5. The apparatus of claim4 wherein said means for separating further comprises:means for mixing aswitching oscillator signal with the separated carrier frequencycomponent to coherently shift the carrier frequency component to thefrequency of one of the separated sideband frequency components; and afilter tuned to the frequency of the selected separated sidebandfrequency component to filter the coherently shifted carrier frequencycomponent.
 6. The apparatus of claim 1 wherein said means for comparingcomprises:a first detector for outputting a voltage signal related tothe amplitude of the carrier frequency component; a second detector foroutputting a voltage signal related to the amplitude of one of thesideband frequency components; and an amplitude comparator fordetermining the component with the larger relative amplitude.
 7. Theapparatus of claim 6 wherein said means for outputting comprises:asingle-pole double-throw switch coupled to the amplitude comparator;said amplitude comparator generating a signal for toggling said switchto output the component with the larger relative amplitude.
 8. Apparatusfor processing an incident electromagnetic signal, comprising:meansresponsive to the incident electromagnetic signal for outputting on asingle channel a sampled signal comprising a carrier frequency componentand two sideband frequency components in the frequency domain; means forreceiving the sampled signal on the single channel and for comparing therelative amplitude of the carrier frequency component and one selectedsideband frequency component; and means coupled to the means forreceiving and comparing for selecting for output the component with thelarger relative amplitude.
 9. The apparatus of claim 8 wherein saidmeans for receiving and comparing comprises:means for mixing a switchingoscillator signal with the carrier frequency component to coherentlyshift the carrier frequency component to the frequency of the oneselected sideband frequency component; a filter tuned to the frequencyof the one selected sideband frequency component to filter thecoherently shifted carrier frequency component; a first detector foroutputting a voltage signal proportional to the amplitude of thecoherently shifted carrier frequency component; a second detector foroutputting a voltage signal proportional to the amplitude of thesideband frequency component; and an amplitude comparator fordetermining the component with the larger detected relative amplitude.10. The apparatus of claim 9 wherein said means for selectingcomprises:a single-pole double-throw switch coupled to said amplitudecomparator; and said amplitude comparator generating a signal whichtoggles said switch in order to output the component with the largerrelative amplitude.
 11. A method for processing an incidentelectromagnetic signal, comprising the steps of:measuring the orthogonalcomponents of electromagnetic power in an incident electromagneticsignal; sampling the orthogonal electromagnetic power components tooutput on a single channel a sampled signal comprised of a carrierfrequency component and two sideband frequency components in thefrequency domain; separating the carrier frequency component from thesideband frequency components; comparing the relative amplitude of thecarrier frequency component and one of the sideband frequencycomponents; and outputting the component with the larger amplitude. 12.Apparatus for processing an incident electromagnetic signal,comprising:means for measuring the orthogonal components ofelectromagnetic power in an incident electromagnetic signal; means forsampling the orthogonal electromagnetic power components to output on asingle channel a sampled signal comprised of a carrier frequencycomponent and two sideband frequency components in the frequency domain;means for separating the carrier frequency component from the sidebandfrequency components; means for comparing the relative phase of thecarrier frequency component and a sideband frequency component; meansfor shifting one component to be in-phase with the other component; andmeans for summing the two components.
 13. The apparatus of claim 12wherein said means for measuring comprises a dual orthogonally polarizedelectromagnetic sensor.
 14. The apparatus of claim 12 wherein said meansfor sampling comprises:a single-pole, double-throw switch coupled toreceive the measured orthogonal electromagnetic power components andoutput the sampled signal; and a switching oscillator connected to saidswitch to cause the switch to sample between the measured orthogonalpower components.
 15. The apparatus of claim 12 wherein said means forseparating comprises:a first filter for receiving the sampled signal,bandpass tuned to separate out the carrier frequency component; and asecond filter for receiving the sampled signal, bandpass tuned toseparate out one sideband frequency component.
 16. The apparatus ofclaim 12 wherein said means for comparing comprises a phase detector fordetermining the phase difference between the carrier frequency componentand a sideband frequency component.
 17. The apparatus of claim 16wherein said means for shifting comprises a phase shifter for shiftingone component an amount substantially equal to the detected phasedifference to be in-phase with the other component.
 18. Apparatus forprocessing an incident electromagnetic signal, comprising:meansresponsive to the incident electromagnetic signal for outputting on asingle channel a sampled signal comprised of a carrier frequencycomponent and two sideband frequency components in the frequency domain;means for receiving the sampled signal on the single channel and forcomparing the relative phase of the carrier frequency component and asideband frequency component; means for shifting one component to bein-phase with the other component; and means for summing the twocomponents.
 19. A method for processing an incident electromagneticsignal, comprising the steps of:measuring the orthogonal components ofelectromagnetic power in an incident electromagnetic signal; samplingthe orthogonal electromagnetic power components to output on a singlechannel a sampled signal comprised of a carrier frequency component andtwo sideband frequency components in the frequency domain; separatingthe carrier frequency component from the sideband frequency component;comparing the relative phase of the carrier frequency component and asideband frequency component; shifting one component to be in-phase withthe other component; and summing the two components.
 20. Apparatus forprocessing an incident electromagnetic signal, comprising:meansresponsive to the incident electromagnetic signal for outputting on asingle channel a sampled signal comprised of a carrier frequencycomponent and two sideband frequency components in the frequency domain;and means for separating the carrier frequency component from thesideband frequency components to output the carrier frequency componentand one of the sideband frequency components.
 21. The apparatus as inclaim 20 wherein said means for outputting comprises:means for measuringorthogonal components of electromagnetic power of the incidentelectromagnetic signal in a single plane perpendicular to the axis ofpropagation of the incident electromagnetic signal; means for samplingthe orthogonal electromagnetic power components to output the sampledsignal.
 22. The apparatus as in claim 21 wherein said means formeasuring comprises a dual orthogonally polarized electromagneticsensor.
 23. The apparatus as in claim 20 further including means forcomparing the relative amplitude and phase of the carrier and sidebandfrequency components of the sampled signal to identify the polarizationcharacteristics of the incident electromagnetic signal.
 24. Theapparatus as in claim 23 wherein said means for comparingcomprises::amplitude measuring means for receiving and comparing therelative amplitude of the carrier and sideband frequency components ofthe sampled signal to determine wave type and orientationcharacteristics; and phase measuring means for receiving and comparingthe relative phase difference between the carrier and sideband frequencycomponents to determine wave rotation characteristic.
 25. The apparatusas in claim 20 wherein said means for separating comprises:a firstfilter for receiving the sampled signal, bandpass tuned to separate outthe carrier frequency component; and a second filter for receiving thesampled signal, bandpass tuned to separate out one sideband frequencycomponent.
 26. The apparatus as in claim 20 further including:means forcomparing the relative amplitude of the carrier and sideband frequencycomponents; and means responsive to the comparison for outputting thecomponent with the larger amplitude.
 27. The apparatus as in claim 26wherein the means for outputting comprises a switch responsive to themeans for comparing for selecting for output the component with thelarger amplitude.
 28. The apparatus as in claim 20 furtherincluding:means for shifting the carrier and sideband frequencycomponents in phase; and means for summing the in-phase carrier andsideband frequency components.
 29. A method processing an incidentelectromagnetic signal, comprising the steps of:measuring theorthogonally polarized components of the incident electromagneticsignal; switching between the measured orthogonal components to outputon a single channel a sampled signal comprised of a carrier frequencycomponent and two sideband frequency components in the frequency domain;and separating the sampled signal to output the carrier frequencycomponent and one of the sideband frequency components.
 30. The methodas in claim 29 including the steps of:measuring and comparing therelative amplitude between the separated carrier component and the onesideband frequency component to determine the wave type and orientationof the polarized electromagnetic signal; and measuring and comparing therelative phase difference between the separated carrier component andthe one sideband frequency component to determine the rotation of thepolarized electromagnetic signal.
 31. The method as in claim 29 furtherincluding the steps of:comparing the relative amplitude of the outputcarrier and sideband frequency components; and responsive to thecomparison, selecting for output the component with the largeramplitude.
 32. The method as in claim 29 further including the stepsof:shifting the carrier and sideband frequency components in phase; andsumming for output the in-phase carrier and sideband frequencycomponents.
 33. The apparatus as in claim 20 further including means forcomparing the relative amplitude of the carrier and one of the sidebandfrequency components of the sampled signal to identify wave type of theincident electromagnetic signal.
 34. The apparatus as in claim 20further including means for comparing the relative amplitude of thecarrier and one of the sideband frequency components of the sampledsignal to identify orientation polarization characteristics of theincident electromagnetic signal.
 35. The apparatus as in claim 20,further including means for comparing the relative phase between thecarrier and one of the sideband frequency components to identifyrotational polarization characteristics of the incident electromagneticsignal.